1. Field of the Invention
This invention concerns light receiving members being sensitive to electromagnetic waves such as light (which herein means in a broader sense those lights such as ultraviolet rays, visible rays, infrared rays, X-rays and .gamma.-rays). More specifically, the invention relates to improved light receiving members suitable particularly for use in the case where coherent lights such as laser beams are applied.
2. Description of the Prior Art
For recording of digital image information, there have been known such a method as forming electrostatic latent images by optically scanning a light receiving member with laser beams modulated in accordance with the digital image information, and then developing the latent images or further applying transfer, fixing or like other treatment as required. Particularly, in the method of forming images by an electrophotographic process, image recording has usually been conducted by using a He, Ne laser or a semiconductor laser (usually having emission wavelength as from 650 to 820 nm), which is small in size and inexpensive in cost as the laser source.
By the way, as the light receiving members for electrophotography being suitable for use in the case of using the semiconductor laser, those light receiving members comprising amorphous materials containing silicon atoms (hereinafter referred to as "a-Si"), for example, as disclosed in Japanese Patent Laid-Open Nos. 86341/1979 and 83746/1981 have been evaluated as being worthy of attention. They have a high Vickers hardness and cause less problems in the public pollution, in addition to their excellent matching property in the photosensitive region as compared with other kinds of known light receiving members.
However, when the light receiving layer constituting the light receiving member as described above is formed as an a-Si layer of a mono-layer structure, it is necessary to structurally incorporate hydrogen or halogen atoms or, further, boron atoms within a range of specific amount into the layer in order to maintain the required dark resistance of greater than 10.sup.12 .OMEGA.cm as for the electrophotography while maintaining their high photosensitivity. Therefore, the degree of freedom for the design of the light receiving member undergoes a rather severe limit such as the requirement for the strict control for various kind of conditions upon forming the layer. Then, there have been made several proposals to overcome such problems for the degree of freedom in view of the design in that the high photosensitivity can effectively be utilized while reducing the dark resistance to some extent. That is, the light receiving layer is so constituted as to have two or more layers prepared by laminating those layers of different conductivity in which a depletion layer is formed to the inside of the light receiving layer as disclosed in Japanese Patent Laid-Open Nos. 171743/1979, 4053/1982 and 4172/1982, or the apparent dark resistance is improved by providing a multi-layered structure in which a barrier layer is disposed between a support and a light receiving layer and/or on the upper surface of the light receiving layer as disclosed, for example, in Japanese Patent Publication Nos. 52178, 52179, 52180, 58159, 58160 and 58161/1981.
However, such light receiving members as having a light receiving layer of multi-layered structure have unevenness in the thickness for each of the layers. In the case of conducting the laser recording by using such members, since the laser beams comprise coherent light, the respective light beams reflected from the free surface of the light receiving layer on the side of the laser beam irradiation and from the layer boundary between each of the layers constituting the light receiving layer and between the support and the light receiving layer (hereinafter both of the free surface and the layer interface are correctively referred to as "interface") often interfere with each other.
The interference results in a so-called interference fringe pattern in the formed visible images which causes defective images. Particularly, in the case of forming intermediate tone images with high gradation, the images obtained become extremely poor in quality.
In addition, as an important point there exist problems that the foregoing interference phenomenon will become remarkably due to that the absorption of the laser beams in the light receiving layer is decreased as the wavelength region of the semiconductor laser beams used is increased.
That is, in the case of two or more layer (multi-layered) structure, interference effects occur as for each of the layers, and those interference effects are synergistically acted with each other to exhibit interference fringe patterns, which directly influence on the transfer member thereby to transfer and fix the interference fringe on the member, and thus bringing about defective images in the visible images corresponding to the interference fringe pattern.
In order to overcome these problems, there have been proposed, for example, (a) a method of cutting the surface of the support with diamond means to form a light scattering surface formed with unevenness of .+-.500 .ANG.-.+-.10,000 .ANG. (refer, for example, to Japanese Patent Laid-Open No. 162975/1983), (b) a method of disposing a light absorbing layer by treating the surface of an aluminum support with black alumite or by dispersing carbon, colored pigment or dye into a resin (refer, for example, to Japanese Patent Laid-Open No. 165845/1982) and (c) a method of disposing a light scattering reflection prevention layer on the surface of an aluminum support by treating the surface of the support with a satine-line alumite processing or by disposing a fine grain-like unevenness by means of sand blasting (refer, for example, to Japanese Patent Laid-Open No. 16554/1982).
Although these proposed methods provide satisfactory results to some extent, they are not sufficient for completely eliminating the interference fringe pattern which forms in the images.
That is, in the method (a), since a plurality of irregularities with a specific t are formed at the surface of the support, occurrence of the interference fringe pattern due to the light scattering effect can be prevented to some extent. However, since the positive reflection light component is still left as the light scattering, the interference fringe pattern due to the positive reflection light still remains and, in addition, the irradiation spot is widened due to the light scattering effect at the support surface to result in a substantial reduction in the resolution power.
In the method (b), it is impossible to obtain complete absorption only by the black alumite treatment, and the reflection light still remains at the support surface. And in the case of disposing the resin layer dispersed with the pigment, there are various problems; degasification is caused from the resin layer upon forming a-Si layer to invite a remarkable deterioration on the quality of the resulting light receiving layer: the resin layer is damaged by the plasma upon forming the a-Si layer wherein the inherent absorbing function is reduced and undesired effects are given to the subsequent formation of the a-Si layer due to the worsening in the surface state.
In the method (c), referring to incident light for instance, a portion of the incident light is reflected at the surface of the light receiving layer to be a reflected light, while the remaining portion intrudes as the transmitted light to the inside of the light receiving layer. And a portion of the transmitted light is scattered as a diffused light at the surface of the support and the remaining portion is regularly reflected as a reflected light, a portion of which goes out as the outgoing light. However, the outgoing light is a component to interfere with the reflected light. In any event, since the light remains, the interference fringe pattern cannot be completely eliminated.
For preventing the interference in this case, attempts have been made to increase the diffusibility at the surface of the support so that no multi-reflection occurs at the inside of the light receiving layer. However, this somewhat diffuses the light in the light receiving layer thereby causing halation and, accordingly, reducing the resolution power.
Particularly, in the light receiving member of the multi-layered structure, if the support surface is roughened irregularly, the reflection light at the surface of the first layer, the reflection layer at the second layer and the positive reflection light at the support surface interfere with each other which results in the interference fringe pattern in accordance with the thickness of each layer in the light receiving member. Accordingly, it is impossible to completely prevent the interference fringe by unevenly roughening the surface of the support in the light receiving member of the multi-layered structure.
In the case of unevenly roughening the surface of the support by the sand blasting or like other method, scattering of the roughness is often caused between the lots and the unevenness in the roughness occurs even in an identical lot thereby causing problems in view of the production control. In addition, relatively large protrusions are frequently formed at random and such large protrusions cause local break down in the light receiving layer.
Further, even if the surface of the support is regularly roughened, since the light receiving layer is usually deposited along with the uneven shape at the surface of the support, the inclined surface on the unevenness at the support are in parallel with the inclined surface on the unevenness at the light receiving layer, where the incident light brings about bright and dark areas. Further, in the light receiving layer, since the layer thickness is not uniform over the entire light receiving layer, a dark and bright stripe pattern results. Accordingly, mere orderly roughening the surface of the support can not completely prevent the occurrence of the interference fringe pattern.
Furthermore, in the case of depositing the light receiving layer of a multi-layered structure on the support having the surface which is regularly roughened, since the interference due to the reflection light at the interface between each of the layers is joined to the interference between the positive reflection light at the surface of the support and the reflection light at the surface of the light receiving layer, the situation is more complicated than the occurrence of the interference fringe in the light receiving member of a single layer structure.
Furthermore, the problem of the interference due to the reflection light in the receiving member of such multi-layered structure also concerns with the surface layer. That is, as can be seen from the foregoing, if the thickness of the surface layer is not uniform, interference occurs due to the reflected light at the interface between the surface layer and the photosensitive layer adjacent thereto to result in trouble in the functioning of the light receiving member.
The unevenness of the thickness of the surface layer is brought about upon forming the surface layer, as well as by abrasion, particularly, partial abrasion during use of the light receiving member. Particularly, in the latter case, it results in the occurrence of the interference pattern as described above and, in addition, also results in the change in the sensitivity, uneven sensitivity or the like over the entire light receiving member.
To eliminate such problems regarding the surface layer, it has been attempted to increase the thickness of the surface layer as much as possible. However this leads to the increase in the residual potential and rather increases the unevenness in the layer thickness of the surface layer. Since the light receiving member having such a surface layer involves the factors for causing problems such as changes in the sensitivity and uneven sensitivity already when the layer has been formed, the member will provide those images that can not be appreciated from the initial time of use.